JP6748109B2 - Suppression of parasitic reaction in flow battery - Google Patents

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority of US Provisional Application No. 62/147,702, filed April 15, 2015, under 35 USC 119, The entire contents of which are incorporated into the present application by reference.

Description of research and development funded by the federal government Not applicable.

The present disclosure relates generally to energy storage, and more specifically to suppressing the occurrence of parasitic reactions in flow batteries and similar electrochemical systems.

Electrochemical energy storage systems such as batteries and supercapacitors have been widely proposed for large-scale energy storage applications. For this purpose, various battery designs such as flow batteries have been studied so far. Flow batteries may be particularly advantageous for large scale applications compared to other types of electrochemical energy storage systems because they allow the power density and energy density parameters to be decoupled from each other.

In general, a flow battery includes a negative active material and a positive active material in respective corresponding electrolytic solutions, and these electrolytic solutions are provided on both sides of a membrane or a separator in an electrochemical cell having a negative electrode and a positive electrode. Each flows separately. The flow battery is charged and discharged by the electrochemical reaction of the active material that occurs inside these two half-cells. As used herein, the terms "active material", "electroactive material", "redox-active material" or variations thereof refer to flow batteries or similar electrical It is used synonymously as a term that refers to a substance whose oxidation state changes during the operation (that is, during charge/discharge) of a chemical energy storage system. Transition metals and their coordination complexes can be particularly desirable active materials because they can assume multiple oxidation states.

Flow batteries hold promise for large-scale energy storage applications, but suffer from shortages of energy storage performance (eg, round trip energy efficiency) and short cycle life, among other factors. There were many The specific problems that cause the lack of energy storage performance are described below. Despite significant research efforts to date, no commercially valuable flow battery technology has been developed.

The oxidation/reduction reaction of the active material in the flow battery is a desirable electrochemical reaction because it contributes to the normal operation of the flow battery during the charge/discharge cycle. In the present specification, such a reaction may be referred to as a “productive reaction”.

In addition to the desired productive reactions, unwanted parasitic reactions may occur within one or both of the two half-cells of a flow battery or similar electrochemical system. As used herein, the term "parasitic reaction" refers to any secondary electrochemical reaction that occurs with a productive reaction. Many of the parasitic reactions may involve components other than the active material in the electrolytic solution. Although there is no theoretical or mechanical regulation, under certain conditions, a component in the electrolytic solution may cause a large overvoltage to cause a parasitic reaction. In other words, under certain conditions, the reducing action or oxidizing action of the components of the electrolytic solution becomes high, which acts on the parasitic reaction. Common parasitic reactions that can occur in electrochemical cells containing aqueous electrolytes are hydrogen evolution, oxygen oxidation, or both. For example, the generation of hydrogen may at least partially discharge the negative electrolyte without changing the positive electrolyte of the electrochemical system. Further, the pH of the electrolytic solution may change due to a parasitic reaction, which may cause the active material in the electrolytic solution to become unstable. Even in a non-aqueous electrolyte solution, the electrolyte solvent may undergo oxidation or reduction due to a parasitic reaction. Further, in both the water-based system and the non-water-based system, the influence of the parasitic reaction may reach the surface of the electrode material or other surfaces (for example, corrosion of carbon or metal, oxidation of separator, etc.).

The discharge due to the parasitic reaction may reduce the operating efficiency of the flow battery and other performance parameters. If a stronger parasitic reaction occurs in one half cell than in the other half cell, an imbalance in the state of charge may occur between the negative electrolytic solution and the positive electrolytic solution. The term "state of charge" (SOC) is a well-understood electrochemical energy storage term, and as used herein, is a reducing species and an oxidizing species at an electrode in a half-cell of an electrochemical system. Refers to the relative amount of. If a charge imbalance occurs between the two electrolytes of the flow battery, mass transfer is restricted at one of the electrodes, which may reduce the efficiency of reciprocal operation. Since the imbalance of charges can be accumulated each time the charging/discharging cycle is completed, there is a possibility that the performance of the flow battery may deteriorate due to a parasitic reaction.

To counter the effects of such parasitic reactions, charge balance can be restored in one or both of the electrolytes. Although various charge balance recovery techniques are currently available, all have been expensive and time consuming to implement. Determining the exact concentrations of reducing and oxidizing species of the active material in the electrolyte is often difficult by itself, which makes the process of restoring charge balance even more difficult.

In view of the above, a flow battery configured to reduce the incidence of parasitic reactions and a method of suppressing parasitic reactions would be highly desirable in the art. The present disclosure meets the above needs and also provides related advantages.

In some embodiments, the present disclosure provides a first half cell including a first electrode, a second half cell including a second electrode, the first half cell and the second half cell. A first bipolar plate overlying and in contact with the first electrode, and a separator overlying and in contact with the second electrode; And a flow battery having two bipolar plates. Here, each of the first electrode and the second electrode covers and contacts each of both surfaces of the separator. Further, while the first electrode or a part of the first bipolar plate contains a dielectric material, the first electrode and the first bipolar plate are continuous in the first half cell. (Contiguous) conductive paths are collectively defined.

In various other embodiments, a flow battery of the present disclosure includes a first half-cell including a first electrode, a second half-cell including a second electrode, the first half-cell and the first half-cell. A separator disposed between the two half-cells. Here, the first electrode and the second electrode respectively cover and contact both surfaces of the separator. Also, the first electrode has a thickness of about 100 microns or less.

In some embodiments, the present disclosure describes methods of suppressing the occurrence of parasitic reactions in electrochemical cells, such as electrochemical cells in flow batteries. The method is disposed between a first half-cell including a first electrode, a second half-cell including a second electrode, and the first half-cell and the second half-cell. A flow battery having a separator, a first bipolar plate that covers and is in contact with the first electrode, and a second bipolar plate that covers and is in contact with the second electrode. Forming, and introducing a dielectric material into the first electrode or a part of the first bipolar plate, even if the introduction is performed, the first electrode and the first bipolar plate are formed. Including introducing a dielectric material into the first electrode or a portion of the first bipolar plate such that the plate and the plate jointly define a continuous conductive path within the first half-cell. Here, the first electrode and the second electrode respectively cover and contact both surfaces of the separator.

In still other various embodiments, a method of suppressing a parasitic reaction in a flow battery includes providing a separator, depositing a catalyst layer on at least a first surface of the separator, and applying the catalyst layer to the catalyst layer. Forming a flow battery having, wherein the flow battery comprises forming a flow battery, wherein the catalyst layer is in contact with a bipolar plate in at least a first half-cell of the flow battery.

The above description generally outlines some of the features of the present disclosure so that the following detailed description can be better understood. Further features and advantages of the disclosure are described below. The above and other advantages and features will be more apparent from the following description.

For a more complete understanding of the present disclosure and its advantages, the following is a description to be read in conjunction with the accompanying drawings, which show specific embodiments of the present disclosure.

1 is a schematic diagram of an exemplary flow battery having a single electrochemical cell. FIG. 3 is a schematic diagram showing an exemplary electrochemical cell configuration having a bipolar plate. FIG. 6 is a schematic diagram showing an exemplary electrochemical cell configuration in which the inside of an electrode is coated with a dielectric material to reduce the incidence of parasitic reactions. FIG. 6 is a schematic diagram showing an exemplary electrochemical cell configuration in which the length of electrodes in the thickness direction is reduced in order to reduce the incidence of parasitic reactions. It is a schematic diagram which shows the exemplary electrochemical cell structure which attached the catalyst layer to the separator in order to reduce the incidence of a parasitic reaction. FIG. 2 is a schematic diagram showing an exemplary electrochemical cell configuration that incorporates a hybrid electrode structure. FIG. 3 is a schematic diagram showing an exemplary electrochemical cell configuration in which the flow path of a bipolar plate is coated with a dielectric material to reduce the incidence of parasitic reactions. FIG. 3 is a schematic diagram illustrating an exemplary electrochemical cell configuration including a dielectric material-based bipolar plate pierced by a plurality of conductor posts.

The present disclosure relates, in part, to flow batteries with reduced incidence of parasitic reactions during operation. The present disclosure also relates, in part, to methods for reducing the incidence of parasitic reactions in flow batteries and similar electrochemical systems.

The present disclosure can be understood more readily by reference to the following description in connection with the accompanying drawings and examples. The accompanying drawings and examples are both part of this disclosure. It will be appreciated that this disclosure is not limited to the particular products, methods, conditions or parameters described and/or illustrated herein. The terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting unless otherwise stated. Similarly, unless stated otherwise, all references herein to a composition are intended to cover both solid and liquid compositions, and further include the composition. Solutions and electrolytes, as well as electrochemical cells, flow batteries and other energy storage systems containing such solutions and electrolytes are intended to be covered. Further, where it is believed that the present disclosure describes an electrochemical cell, flow battery or other energy storage system, implicitly also a method of operating the electrochemical cell, flow battery or other energy storage system. Please recognize it as explaining.

Also, although some features of the disclosure are described herein in the context of separate embodiments for clarity, they may be combined together in a single embodiment. It will be appreciated that you can. That is, it is contemplated that individual embodiments may be combined with any one or more other embodiments, unless such combinations are explicitly incompatible or explicitly excluded, and such combinations are entirely separate. Of the present invention. Conversely, for the sake of brevity, the various features of this disclosure may be described in the context of a single embodiment, although it is possible that these features may be provided separately or in any smaller combination. is there. Furthermore, although a particular embodiment may be described as part of a series of steps or as part of a more comprehensive structure, each step or substructure is considered to be an independent embodiment in its own right. Is also possible.

Unless stated otherwise, it is understood that when listing elements, each and every combination of elements listed and each element in the list is to be construed as a separate embodiment. For example, a list of embodiments designated "A, B or C" includes "A", "B", "C", "A or B", "A or C", "B or C" or "A". , B or C”.

In this disclosure, the singular articles "a", "an" and "the" refer to the corresponding plural unless the context clearly indicates otherwise. References to a particular numerical value are also inclusive of at least that particular value. Thus, for example, "a material" refers to at least one such material and its equivalents.

In general, use of the term "about" indicates an approximation that may vary depending on the desired properties sought to be achieved by the disclosed subject matter, and shall be construed accordingly in function and context. Is. Therefore, those skilled in the art will be able to obtain a certain range of variation depending on the individual situation. A typical technique for defining the variation allowed by the term "about" is to use the number of significant figures in expressing a particular value. Alternatively, the range of variation allowed by the term "about" can be defined by providing steps in a series of values. Further, all ranges in this disclosure are inclusive and combinable, and when reference is made to a value defined by a range, the reference includes all individual values within the range. is there.

As mentioned above, it may be highly desirable to have an energy storage system that can operate on a large scale while maintaining high efficiency values. Flow batteries have been of great interest in this regard, but their operating characteristics still have considerable room for improvement. Parasitic reactions can have a very serious impact on the operational performance of flow batteries and other electrochemical systems. For example, a parasitic reaction can cause an imbalance in the state of charge between two electrolytes of a flow battery, which can affect battery performance over time and repeated charge and discharge cycles. In addition, parasitic reactions can cause unwanted pH changes in one or more electrolytes. Due to a number of operational issues, traditional flow battery designs may have difficulty dealing with parasitic reactions.

As a result of considering the adverse effects of these parasitic reactions and the difficulty of coping with the parasitic reactions, the present inventor has realized that it is highly desirable to minimize the incidence of parasitic reactions in the flow battery. .. In the conventional flow battery design, except for changing the operating condition of the flow battery so as to prevent the overvoltage from becoming excessive and the accompanying parasitic reaction, and completely replacing the battery components. However, no mechanism is provided that can be found to minimize the incidence of parasitic reactions. However, by changing the operating conditions so as to prevent the generation of an excessive overvoltage that causes a parasitic reaction, the productive reaction of the desired active material may not occur at all or may not occur at a sufficient reaction rate. Therefore, changing the operating conditions of a flow battery to suppress parasitic reactions can be an unacceptable approach in some situations. Before further describing the inventor's discovery of an approach to reducing the incidence of parasitic reactions in a flow battery, an exemplary flow battery configuration and its operating characteristics are described in more detail below.

Unlike common battery technologies where active materials and other components are contained in a single assembly (eg, lithium-ion batteries, nickel hydride batteries, lead acid batteries, etc.), flow batteries are redox active energy storage materials in storage tanks. Are transported (eg, by pumping) through an electrochemical stack containing one or more electrochemical cells. This design feature allows the electrical energy storage system power supply to be decoupled from the energy storage capacity, thus providing significant design flexibility and cost optimization. FIG. 1 is a schematic diagram of an exemplary flow battery having a single electrochemical cell. Although FIG. 1 shows a flow battery with a single electrochemical cell, methods for connecting a plurality of electrochemical cells to each other are known and will be described below.

As shown in FIG. 1, the flow battery system 1 has an electrochemical cell. This electrochemical cell is characterized in that it has a separator 20 between its two electrodes 10, 10'. As used herein, the terms "separator" and "membrane" refer to a material that is disposed between the positive and negative electrodes of an electrochemical cell and that has ionic conductivity and electrical insulation. .. The electrodes 10, 10' are formed of a suitable conductive material such as metal, carbon, graphite, etc., and the materials of both electrodes may be the same or different. Although the electrodes 10, 10 ′ are shown spaced apart from the separator 20 in FIG. 1, in a more specific embodiment, the electrodes 10, 10 ′ may be placed in contact with the separator 20. Yes (see below and Figure 2). This contact may be direct in some cases, as shown in FIG. 2, and in other cases indirect, such as with a carbon cloth or carbon foam intervening. The material forming the electrodes 10, 10 ′ may be porous, which increases the contact surface area with the electrolytic solution containing the first active material 30 and the electrolytic solution containing the second active material 40. .. The first active material 30 and the second active material 40 are materials that can circulate between an oxidized state and a reduced state.

The pump 60 is for transporting the first active material 30 from the tank 50 to the electrochemical cell. The flow battery also suitably includes a second tank 50' containing a second active material 40. The second active material 40 may be the same material as the first active material 30 or may be a different material. The second pump 60' is for transporting the second active material 40 to the electrochemical cell. Also, a pump may be used to transport the active material 30,40 back from the electrochemical cell to the tank 50,50' (not shown in Figure 1). In addition, the first active material 30 and the second active material 40 can be appropriately transported into and out of the electrochemical cell by another method that affects fluid transportation, such as siphon. Also shown in FIG. 1 is a power source or load 70. The load 70 completes the electrochemical cell circuit and allows the user to store or store electricity during operation of the circuit.

It is to be understood that FIG. 1 illustrates a particular flow battery configuration and is not intended to be limiting. Accordingly, a flow battery consistent with the spirit of the present disclosure may differ from the configuration of FIG. 1 in various respects. As an example, a flow battery system can include one or more active materials that are gases dissolved in a solid, gas and/or liquid. The active material can be stored in a tank or container that is open to the atmosphere or simply provided with a vent to the atmosphere.

As mentioned above, a plurality of electrochemical cells may be combined with each other to form an electrochemical stack in order to increase the energy storage/release rate during operation. The amount of energy released is determined by the total amount of active material present. In the electrochemical stack, a bipolar plate is provided between adjacent electrochemical cells so as to block fluid communication while ensuring electrical communication between the adjacent electrochemical cells. In this way, the bipolar plate encloses each electrolytic solution in each electrochemical cell. Bipolar plates are generally made of a conductive material, but have no overall fluid communication. Suitable materials can include carbon, graphite, metals or combinations thereof. It is also possible to disperse a conductive material in a non-conductive polymer to manufacture a bipolar plate. Examples of such a conductive material include carbon particles, carbon fibers, metal particles, metal fibers, carbon nanotubes, or any one or a combination thereof. Bipolar plates can be made of the same type of conductive material as the electrodes of an electrochemical cell, but the electrodes have many continuous holes that allow the complete passage of the electrolyte flow, whereas bipolar plates do not. It does not have multi-continuous porosity. However, it should be recognized that the bipolar plate is not necessarily a completely non-porous object. The bipolar plate is porous in terms of material or structure and can increase the surface area that the electrolyte can contact, but this porosity means that the electrolyte flows into the adjacent electrochemical cell. It terminates before the position where it is possible. For example, a bipolar plate may have multiple channels designed to prevent electrolyte from contacting the bipolar plate more efficiently, while prohibiting passage through the bipolar plate to adjacent cells. You can also have. The bipolar plate can be directly contacted with the electrode in the electrochemical cell in which the bipolar plate is installed, or can be contacted with a conductive material such as carbon foam, carbon cloth or carbon net.

FIG. 2 is a schematic diagram showing an exemplary electrochemical cell configuration including a bipolar plate. Note that the same reference symbols are used as appropriate for the same elements as in FIG. Referring to FIG. 2, each of the negative half-cell 80 and the positive half-cell 80 ′ is disposed on each of the opposing sides of the separator 20. Negative half-cell 80 has an electrode 10 (ie, an anode) that contacts separator 20 at interface 12 and a bipolar plate 90 that contacts an opposing surface of electrode 10 at interface 14. Similarly, a positive half-cell 80' has an electrode 10' (ie, cathode) that abuts the opposite surface of the separator 20 at the interface 12' and an opposite side of the electrode 10' at the interface 14'. And a bipolar plate 90' that abuts the face of the. In an alternative embodiment, the electrodes 10, 10 ′ may have carbon foam or carbon cloth interposed between them and the separator 20. The plurality of flow paths 82 partially extend inside the bipolar plates 90 and 90' to improve the degree of contact with the electrolytic solution. FIG. 2 shows that the flow paths 82 are formed substantially linearly and are arranged at regular intervals. However, each flow path 82 may have any shape, such as a tortuous path, or may be interconnected with each other, or both, and/or distributed in a random or gradient pattern. Please be aware that you may. In any case, the back surfaces 84, 84' of the bipolar plates 90, 90' do not substantially allow passage of the electrolytic solution, and the occurrence of crossover between adjacent electrochemical cells is suppressed. .. For clarity, the fluid flow details shown in FIG. 1 are not shown in FIG. However, aspects of incorporating the electrochemical cell configuration of FIG. 2 into FIG. 1 and aspects of incorporating multiple electrochemical cells into an electrochemical stack and connecting to a fluid distribution manifold can be readily understood. Will. For purposes of this specification, the electrochemical cell configuration of FIG. 2 will be considered a representative example of a cell configuration used in conventional flow batteries.

Returning now to the suppression of parasitic reactions, the present inventor has shown that in conventional electrochemical cells, most of the productive reactions are on the interface between the electrode and the separator (ie interfaces 12, 12'). Or, it was discovered that it occurred at a position close to this interface. On the other hand, in many cases, the parasitic reaction occurs at a position inside the electrode or at another conductive surface far away from the separator. Furthermore, parasitic reactions can also occur when the electrolyte contacts the conductive material of the bipolar plate. Thus, the inventor has discovered that within an electrochemical cell, parasitic reactions occur at one or more locations that are not proximate to the separator.

As a solution to reduce the incidence of parasitic reactions at one or more locations that are not in close proximity to the separator, the inventor has improved the structure of the electrodes of the electrochemical cell, the bipolar plate, or both to provide a good We have discovered various techniques that can promote the production of productive reactions and reduce the incidence of unwanted parasitic reactions while remaining conductive. Although the following disclosure shows that each of the electrode and bipolar plate modifications are made separately, both of these structures can be modified simultaneously in an electrochemical cell, and such modifications are Should be recognized as consistent with the spirit of the present disclosure. By improving both the electrodes and the bipolar plates of the electrochemical cell, the incidence of parasitic reactions can be further reduced.

In particular, the present inventor has discovered that the incidence of parasitic reaction can be reduced by reducing the contact area between at least one of the electrode and the bipolar plate and the electrolytic solution. The following describes in more detail suitable techniques that can reduce the contact area.

The inventor has discovered, as one of the suitable approaches to reduce the incidence of parasitic reactions at the electrode, involves infusing a dielectric material inside the electrode. By coating the inner surface inside the porous electrode with a dielectric material, the possibility that most of the electrode will come into contact with the electrolyte can be eliminated. By eliminating the possibility of non-productive or less productive parts of the electrode coming into contact with the electrolyte, the spread of parasitic reactions can be reduced. The surface of the electrode located at the interface with the separator remains uncovered, and the electrode can be left with a portion that can freely promote the productive reaction. Since the surface coating with the dielectric material is carried out only in the pores of the electrode, the circulation of the electrolyte through the electrode is not significantly hindered by this coating. Furthermore, since the surface coating with the dielectric material is performed only inside, the conductivity of the entire electrode is still maintained, and it is possible to secure a continuous conductive path in conjunction with the bipolar plate. it can.

FIG. 3 is a schematic diagram showing an exemplary electrochemical cell configuration in which the inside of the electrode is coated with a dielectric material in order to reduce the incidence of parasitic reactions. The electrochemical cell configuration of FIG. 3 is similar to that of FIG. 2 except that the interior of the electrode 10 is provided with a dielectric coating 100, which can be better understood with reference to FIG. Let's do it. As mentioned above, the uncoated portion of the electrode 10 provides an effective surface where productive reactions may still occur and/or maintain electrical contact with the bipolar plate 90. The effective surface for such productive reactions and electrical contact is retained because the dielectric material is not in contact with the separator 20 or the bipolar plate 90. Although only electrode 10 is shown in FIG. 3 as having a dielectric-coated interior, in some embodiments of the present disclosure, electrode 10' or both electrodes 10, 10' are dielectric-coated. It should be appreciated that it may have an interior. In some embodiments, electrode 10 and dielectric coating 100 may be present in the negative half-cell of an electrochemical cell.

Coating the interior of the electrode with a dielectric material increases the relative rate at which productive reactions can occur at the electrode. By disabling parts of the electrode that are not sufficiently close to the separator, the relative rate at which productive reactions can occur at the electrode is increased. In light of this feature, the present inventor further reduced the through-plane thickness of the electrode by coating the inside of the electrode with a dielectric material as described above, thereby reducing the electrode thickness. I also noticed that the ratio of the effective part to the separator increased. Therefore, in another aspect of the present disclosure, the present inventor has found that the incidence of the parasitic reaction can be similarly reduced by reducing the length of the electrode in the thickness direction (FIGS. 4 and 5). And the description of these figures below). That is, the present inventor has discovered that the incidence of the parasitic reaction can be similarly reduced by making the electrode thin without using the dielectric material.

FIG. 4 is a schematic diagram showing an exemplary electrochemical cell configuration in which the length of electrodes in the thickness direction is reduced in order to reduce the incidence of parasitic reactions. The electrochemical cell configuration of FIG. 4 is similar to that of FIG. 2 except that the thickness of the electrode 10 is reduced, which may be better understood with reference to FIG. In FIG. 4, the electrode area in the vicinity of the separator 20 is increased by reducing the length of the electrode 10 in the thickness direction, and thus the incidence of parasitic reaction is reduced. Although shown in FIG. 4 as reducing only the thickness of the electrode 10 in the thickness direction, in some embodiments of the present disclosure, the thickness of the electrode 10′ or both electrodes 10, 10′ may be reduced. It should be appreciated that can be reduced. Further, in various embodiments of the present disclosure, electrodes 10, 10' may have substantially the same thickness, or electrodes 10, 10' may have different thicknesses. In some embodiments, a suitably thin electrode can have a thickness of about 100 microns or less, eg, about 1 micron to about 100 microns, about 20 microns to about 100 microns, about 50 microns to about 50 microns. It can have a thickness in the range of 100 microns.

In various other embodiments, a suitably thin electrode can have a thickness of less than about 1 micron. In more specific embodiments, a suitably thin electrode can have a thickness in the range of about 1 nm to about 100 nm, about 1 nm to about 10 nm, about 10 nm to about 50 nm, or about 5 nm to about 20 nm. In some embodiments, one or more graphene sheets can make up an electrode. Graphene may be a particularly suitable material for forming an electrode of a flow battery because of its high in-plane conductivity and mechanical strength and its thin layer thickness.

Although an electrode of suitable thickness allows more parts of the electrode to be in close proximity to the separator to reduce the incidence of parasitic reactions, such thin electrode materials are not It is difficult to handle and may be less durable than thick electrodes. Therefore, the inventor has discovered a further technique for reducing the incidence of parasitic reactions by varying the thickness-wise length of a conventional electrode, while still not improving the electrode with a dielectric material. .. More specifically, the inventor has discovered that the conventional electrode abutting the separator can be replaced by a catalyst layer deposited on the separator. The catalyst layer may constitute a continuous or discontinuous coating on the separator. The catalyst layer can, in effect, function as an extremely thin and porous electrode, on which the productive reaction can occur very close to the separator and the electrical connection to the bipolar plate. It can be constructed. Suitable materials for inclusion in the catalyst layer include high surface area materials such as carbon nanotubes, carbon powder, graphite and the like.

FIG. 5 is a schematic diagram showing an exemplary electrochemical cell configuration with a catalyst layer deposited on the separator to reduce the incidence of parasitic reactions. The electrochemical cell configuration of FIG. 5 is similar to that of FIG. 2 except that the electrode 10 is replaced with a catalyst layer 11, which may be better understood with reference to FIG. Also in FIG. 5, since the thickness of the catalyst layer 11 is small, the area of the “electrode” in the vicinity of the separator 20 in which the productive reaction can occur more effectively is increased. For example, in some embodiments, catalyst layer 11 can be about 100 microns or less. Although only electrode 10 is shown in FIG. 5 as being replaced with catalyst layer 11, some embodiments of the present disclosure may replace electrode 10′ or both electrodes 10, 10′ with a catalyst layer. Please be aware that. If both electrodes 10, 10' are replaced by a catalyst layer, the catalyst material may be the same or different between the half-cells 80, 80'.

In some embodiments, the catalyst layer can include multiple carbon nanotubes. Carbon nanotubes have high conductivity and can function as an extremely thin and porous matrix. In some embodiments, carbon nanotubes can be mixed with catalyst particles (eg, metal nanoparticles) in the catalyst layer. In some embodiments, carbon nanotubes can be deposited as a layer whose longitudinal axis extends substantially parallel to the separator. In this configuration, the carbon nanotubes can provide high in-plane conductivity near the separator to facilitate productive reactions and still establish electrical connection with the bipolar plate. Suitable techniques for aligning carbon nanotubes will be apparent to those skilled in the art.

Suitable carbon nanotubes for inclusion in the catalyst layer can include single-wall carbon nanotubes, double-wall carbon nanotubes, multi-wall carbon nanotubes, or any combination thereof. Carbon nanotubes become metallic, semi-metallic, or semiconducting depending on their chirality. Nomenclature for specifying the chirality of carbon nanotubes has been established and is well known in the art. According to this, the chirality of carbon nanotubes is obtained when n and m are two integers representing a cutting direction (cut) and a rounding direction (wrapping) when forming hexagonal graphite into a tubular structure. , Identified by the index pair (n,m). In addition to chirality, the diameter of carbon nanotubes also affects their electrical conductivity and thermal conductivity values. Generally, in a multi-walled carbon nanotube, a reaction may occur across each nanotube layer, and thus may have a more complicated electric conductivity/thermal conductivity profile than a single-walled carbon nanotube. On the other hand, in the single-walled carbon nanotube, the electric conductivity and the thermal conductivity profile do not change between different parts. Thus, because single-walled carbon nanotubes have favorable conductivity values, in more specific embodiments of this disclosure, the catalyst layer may include multiple single-walled carbon nanotubes.

In yet another alternative configuration, the present inventor combines the two concepts of catalyst layer and dielectric material with each other into a hybrid electrode structure having a thickness-thickness closer to that of a conventional electrode. I discovered that I can do it. As will be explained in more detail below, such an electrode structure advantageously allows for a narrower range in which productive reactions can occur more effectively while maintaining the ability to establish an electrical connection with the bipolar plate. The area close to the separator can be maintained.

In a more specific embodiment, the hybrid electrode structure includes a conductive medium disposed on a first side of the conductive mesh and a dielectric material disposed on a second side of the conductive mesh. Can be included. The placement of the conductive mesh and the dielectric material can be done so that the conductive medium can contact the separator and undergo a highly reactive and productive reaction. The hybrid electrode structure also includes a plurality of conductor posts extending through the dielectric material from the conductive mesh to the bipolar plate, the conductor posts allowing the electrochemical cell to be contacted with the dielectric material in contact with the bipolar plate. It is possible to secure a continuous conductive path inside. In the hybrid electrode structure, if the conductor posts were not present and did not contact the bipolar plate, the dielectric material would prevent the electrical connection between the electrode and the bipolar plate from being established.

FIG. 6 is a schematic diagram showing an exemplary electrochemical cell configuration having a hybrid electrode structure therein. The electrochemical cell configuration of FIG. 6 is similar to that of FIG. 2 except that the electrode 10 is replaced with a hybrid electrode 13, which may be better understood by reference to FIG. The hybrid electrode 13 includes a conductive mesh 15 having a conductive material 16 on one surface and a dielectric material 17 on the other surface. The conductive material 16 contacts the separator 20 and the dielectric material 17 contacts the bipolar plate 90. A conductor post 18 extends through the dielectric material 17 from the conductive mesh 15 to the bipolar plate 90 to establish an electrical connection with the bipolar plate. Although only electrode 10 is shown in FIG. 6 as being replaced with hybrid electrode 13, in some embodiments of the present disclosure, electrode 10′ or both electrodes 10, 10′ may be replaced with a hybrid electrode. Please recognize that here as well. Suitable materials for the conductive material 16 can include any of the conductive materials disclosed herein, such as the materials utilized in conventional electrodes. Similarly, the conductive mesh 15 can be formed of any suitable conductive material.

Turning now to the bipolar plate, the present inventor has discovered various approaches to reduce the incidence of parasitic reactions by reducing the amount of conductive material in the bipolar plate that contacts the electrolyte. Some of these approaches are similar to those for the electrodes described above, and may be better understood with reference to the above approaches. More specifically, the inventor can reduce the incidence of parasitic reactions by incorporating a dielectric material in a portion of the bipolar plate so as not to completely impair the conductivity of the bipolar plate. I have found In the following, suitable locations within the bipolar plate that can be modified with dielectric materials to reduce the incidence of parasitic reactions are described in more detail.

In one configuration, it has been discovered that the incidence of parasitic reactions can be reduced by coating at least a portion of the interior of the bipolar plate. More specifically, the inventor has discovered that by coating at least a portion of the flow path inside the bipolar plate with a dielectric material, the degree of contact between the electrolyte and the conductive material of the bipolar plate can be significantly reduced. did. As described above, this limits the force of the conductive material for promoting the parasitic reaction, but does not impair the conductivity of the bipolar plate. This approach is somewhat similar to the above approach of coating the interior of the electrode with a dielectric material.

FIG. 7 is a schematic diagram showing an exemplary electrochemical cell configuration in which the flow path of the bipolar plate is coated with a dielectric material to reduce the incidence of parasitic reactions. The electrochemical cell configuration of FIG. 7 is similar to that of FIG. 2 except that the inside of the flow path 82 of the bipolar plate 90 is covered with the coating layer 86, and FIG. 7 will be further described with reference to FIG. You can understand it well. In various embodiments, the fluid can be kept in and out of the channel 82 by limiting the thickness of the coating layer 86 so that the channel 82 is not completely blocked. Even with the coating layer 86 present in the flow channel 82, electrical contact between the electrode 10 and the bipolar plate 90 is still maintained at the interface 14 to facilitate electrical communication between adjacent electrochemical cells. is made of.

Also, as an alternative configuration, the inventor has discovered that the amount of conductive material in the bipolar plate can be significantly reduced to reduce the incidence of parasitic reactions. In particular, the present inventor replaces most of the conductive material in the bipolar plate with the dielectric material, leaving the conductive material only in a limited area to establish the conductivity with the electrodes, and to improve the conductivity between the adjacent electrochemical cells. It has been discovered that it can facilitate electrical communication. More specifically, the inventor provides a mass of dielectric material in the form of a conventional bipolar plate with a plurality of conductor posts therethrough to ensure a continuous conductive path within the half-cell. By doing so, it has been discovered that a de facto bipolar plate can be manufactured. This bipolar plate configuration will be described in more detail below in connection with FIG. In some configurations, in bipolar plates made primarily of dielectric material, the internal flow paths are omitted and the conductor posts maintain sufficient conductivity for the bipolar plate to function as intended. Can be able to.

FIG. 8 is a schematic diagram illustrating an exemplary electrochemical cell configuration in which multiple conductor posts extend through a dielectric material-based bipolar plate. In some embodiments, the conductor posts 94 may be conductors, which minimizes the surface area of the conductor material in contact with the electrolyte at the interface 14 to minimize the surface area where parasitic reactions occur. Can be suppressed. The number of conductor posts 94 extending through the dielectric-based bipolar plate 92 can be selected to ensure sufficient conductivity while keeping the incidence of parasitic reactions below a predetermined level. .. Therefore, the number of conductor posts 94 shown in FIG. 8 should not be considered limiting. Further, any arrangement of conductor posts 94 within the dielectric material-based bipolar plate layer 92 is possible, and the regular arrangement shown in FIG. 8 should not be considered limiting. The electrochemical cell configuration of FIG. 8 is similar to that of FIG. 2 except for the presence of the dielectric material based bipolar plate 92 and conductor posts 94, which can be better understood with reference to FIG. Ah

As described above, the various electrochemical cell configurations described above can desirably reduce the incidence of parasitic reactions that occur in the electrochemical cell. More specifically, the first electrode and/or the first bipolar plate can have an effective area sized such that the ratio of productive reactions to parasitic reactions during operation of the flow battery is greater than 5. .. Further, the generation ratio of the productive reaction to the parasitic reaction can be further increased. In some embodiments, the ratio of productive reaction to parasitic reaction is about 10 or more, about 20 or more, about 30 or more, about 40 or more, about 50 or more, about 100 or more, about 200 or more, about 500 or more, or It can be about 1000 or more. Depending on the application, the appropriate value of the ratio of productive reaction to parasitic reaction can vary. Thus, in designing a particular electrochemical cell, any number of the features described above may be incorporated to achieve a given value of the productive to parasitic incidence ratio. The appropriate generation ratio for a given application can be determined based on optimization of cell resistance versus current efficiency. For example, the total effective area of the half-cell can be reduced until the cell resistance exceeds a threshold, and then the current efficiency for this cell shape can be determined. If the current efficiency is sufficient, this cell configuration can be preferably used. In other words, at least about 95% of the current in the half-cell can result from the productive reaction, and in some embodiments at least about 99% of the current in the half-cell can result from the productive reaction. ..

In embodiments where a dielectric material (ie, an insulator) is used to reduce the incidence of parasitic reactions, a wide range of generally non-conductive materials can be used as the dielectric material. In some embodiments, suitable dielectric materials can include plastics (ie, polymers such as fluorinated polymers), ceramics and fluorinated hydrocarbons. Polytetrafluoroethylene may be mentioned as one of the particularly suitable fluorinated polymers. Other suitable polymers include, for example, polyethylene, polypropylene, neoprene and the like. As used herein, the term "ceramic" refers to a non-metallic inorganic material, which may be crystalline, partially crystalline, or substantially or completely amorphous. In some embodiments, suitable ceramics include oxides, carbides, nitrides, borides, and the like. Specific examples of exemplary ceramics include, for example, beryllium oxide, barium titanate, boron nitride, silicon carbide, titanium carbide, and the like.

Suitable techniques for introducing the dielectric material into or on the electrode or bipolar plate are not particularly limited, but in some embodiments, the dielectric material is dissolved in a solvent and applied by spraying or brushing to coat. The dielectric material can be applied to the electrodes or bipolar plates by any of the following techniques or by dip coating. In other embodiments, the ceramic can be deposited by thin film deposition techniques such as chemical vapor deposition, atomic layer deposition. If a catalyst layer is present, it can be provided in a similar manner.

The electrodes are for passing an electric current from an external circuit to a position in the electrochemical cell where electrochemical energy conversion occurs. Electrodes can undergo electrochemical reactions at their surface, including both productive and non-productive reactions. In some embodiments, the electrodes can include a catalyst. In an alternative embodiment, one or more electrodes of the flow cell can consist essentially of the catalyst layer. Suitable conductive materials for inclusion in the electrodes of flow batteries include, for example, carbon and/or metals such as gold, silver, titanium, platinum. Other suitable electrically conductive materials can include, for example, steel, zinc, tantalum, palladium, tin, nickel, copper, iridium, rhodium, ruthenium, boron nitride, tungsten carbide, boron doped diamond and degenerately doped semiconductors. In some embodiments, suitable electrodes can take the form of porous sheets containing one or more of the above materials. The electrode thickness suitable for various configurations is described in detail above.

In some embodiments, the flow batteries of the present disclosure can include an active material that is a coordination complex in one or more electrolytes. As used herein, the terms "coordination complex" and "coordination compound" refer to any compound having a metal covalently bound to one or more ligands. Transition metals can variably assume multiple oxidation states and may therefore be particularly desirable for use in active materials for flow batteries. By circulating a plurality of possible oxidation states of the transition metal, chemical energy can be converted into electric energy. In alternative embodiments, lanthanide metals can be used as well in this regard. Particularly desirable transition metals for inclusion in flow batteries include, for example, Al, Cr, Ti and Fe. For the purposes of this disclosure, Al is considered to be a transition metal. In some embodiments, the coordination complex within the flow battery can have at least one catecholate or substituted catecholate ligand. Sulfonated catecholate ligands can be particularly desirable ligands because they can promote the solubility of coordination complexes containing the same.

Other ligands that may be present in the coordination complex, alone or with one or more catecholate or substituted catecholate ligands include, for example, ascorbates, citrates, glycolates, polyols, Gluconate, hydroxyalkanate, acetate, formate, benzoate, malate, maleate, phthalate, sarcosinate, salicylate, oxalate, urea, polyamine, aminophenolate, Examples include acetylacetonate and lactate. Here, when chemically feasible, such a ligand is used as a C _1-6 alkoxy group, a C _1-6 alkyl group, a C _1-6 alkenyl group, a C _1-6 alkynyl group, 5-membered or 6-membered aryl group or heteroaryl group, boronic acid or its derivative, carboxylic acid or its derivative, cyano, halide, hydroxyl, nitro, sulfonate, sulfonic acid or its derivative, phosphonate, It will be appreciated that it can be optionally substituted by at least one group selected from phosphonic acid or its derivatives or glycols such as polyethylene glycol. Alkanes include all of their α, β and γ forms. Polyamines include, but are not limited to, ethylenediamine, ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA).

Other examples of ligands that may be present include monodentate, bidentate and/or tridentate ligands. Examples of monodentate ligands that may be present in the coordination complex include, for example, carbonyl or carbon monoxide, nitrides, oxo, hydroxo, water, sulfides, thiols, pyridines, pyrazines and the like. Examples of bidentate ligands that may be present in the coordination complex include, for example, bipyridine, bipyrazine, ethylenediamine, diols (such as ethylene glycol), and the like. Examples of tridentate ligands that may be present in the coordination complex include, for example, terpyridine, diethylenetriamine, triazacyclononane, tris(hydroxymethyl)aminomethane and the like.

The active material in the flow battery may be dissolved and present in the aqueous electrolytic solution. As used herein, the term “aqueous electrolyte solution” means a uniform liquid phase in which water is a main solvent and the active material is at least partially solubilized (ideally completely solubilized). Refers to. This definition includes both aqueous solutions and solutions containing a water-miscible organic solvent in the aqueous phase as a minor component.

Exemplary water-miscible organic solvents that may be present in the aqueous electrolyte include, for example, alcohols and glycols, and optionally one or more of the below-described surfactants and other components may be present. .. In a more specific embodiment, the aqueous electrolyte can contain at least about 98 wt% water. In other more specific embodiments, the aqueous electrolyte is at least about 55% by weight water, at least about 60% by weight water, at least about 65% by weight water, at least about 70% by weight water, at least about 70% by weight. It may contain 75% by weight water, at least about 80% by weight water, at least about 85% by weight water, at least about 90% by weight water, or at least about 95% by weight water. In some embodiments, the aqueous electrolyte solution does not contain a water-miscible organic solvent and may contain only water as a solvent.

In a further embodiment, the aqueous electrolyte can include a viscosity modifier, a wetting agent, or any combination thereof. Suitable viscosity modifiers can include, for example, corn starch, corn syrup, gelatin, glycerol, guar gum, pectin and the like. Other suitable examples will be familiar to those skilled in the art. Suitable wetting agents can include, for example, various nonionic surfactants and/or detergents. In some or other embodiments, the aqueous electrolyte can further include glycols or polyols. Suitable glycols may include, for example, ethylene glycol, diethylene glycol and polyethylene glycol. Suitable polyols can include, for example, glycerol, mannitol, sorbitol, pentaerythritol and tris(hydroxymethyl)aminomethane. The inclusion of any of these components in the aqueous electrolytic solution is, for example, to promote the dissolution of the coordination complex or an active material similar thereto and/or to transport the aqueous electrolytic solution in the flow battery. It can help reduce the viscosity of the electrolyte.

In addition to the solvent and the coordination complex as the active material, the aqueous electrolyte can also include one or more mobile ions (ie, exogenous electrolyte). In some embodiments, suitable mobile ions can include protons, hydronium ions or hydroxide ions. In various other embodiments, mobile ions other than protons, hydronium ions or hydroxide ions can be present alone or in combination with protons, hydronium ions or hydroxide ions. Such alternative mobile ions include, for example, alkali metal or alkaline earth metal cations (eg, Li ⁺ , Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ and Sr ²⁺ ), and halides (eg, , F ⁻ , Cl ^−, or Br ⁻ ). Other suitable mobile ions include, for example, ammonium and tetraalkylammonium ions, chalcogenides, phosphates, hydrogen phosphate, phosphonates, nitrates, sulfates, nitrites, sulfites, perchlorates, tetrafluoro. Mention may be made of borates, hexafluorophosphates and any combination thereof. In some embodiments, protons, hydronium ions or hydroxide ions can make up less than about 50% of the mobile ions. In various other embodiments, the proton, hydronium or hydroxide ion is less than about 40%, less than about 30%, less than about 20%, less than about 10%, less than about 5%, or about 2% of the mobile ions. Can constitute less than %.

Flow batteries can provide a durable charge/discharge cycle with a duration of several hours. Therefore, flow batteries may be used to provide a mechanism to smooth energy supply/demand profiles and stabilize intermittently generated assets (eg, from renewable energy sources such as solar and wind energy). it can. Thus, it should be understood that various embodiments of the present disclosure contemplate energy storage applications in which such long charge or discharge durations are desirable. For example, in a non-limiting example, a flow battery of the present disclosure is connected to a power grid to provide renewable energy integration, peak load shift, grid firming, base. It enables load generation and consumption, energy arbitrage, deferring of transmission and distribution assets, weak grid support, frequency regulation, or any combination of these. When not connected to the grid, the flow battery of the present disclosure can be used as a power source for remote camps, frontline operations bases, gridless telecommunications, remote sensors, etc., and any combination thereof. it can. Further, while the disclosure herein is generally directed to flow batteries, other electrochemical energy storage media are also described herein, particularly electrochemical energy storage media that utilize a stationary electrolyte. It should be understood that the electrolytes and coordination complexes described can be incorporated.

In some embodiments, a flow battery includes a first chamber in contact with a first aqueous electrolyte to contain a negative electrode and a second chamber in contact with a second aqueous electrolyte to contain a positive electrode. And a separator disposed between the first electrolytic solution and the second electrolytic solution. Each of these chambers serves as a separate reservoir within the cell so that the first and/or second electrolyte may pass through these chambers to contact their respective electrodes and separators. Circulate. Each chamber and its associated electrodes and electrolyte form a corresponding half-cell. The separator has several functions including, for example: That is, (1) it functions as a barrier that prevents mixing of the first electrolytic solution and the second electrolytic solution, (2) electrically insulates so as to reduce or prevent a short circuit between the positive electrode and the negative electrode, and ( 3) facilitate ion transfer between the positive and negative electrolyte chambers, thereby balancing electron transport during charge and discharge cycles. On the surface of the negative electrode and the positive electrode, an electrochemical reaction can be generated during the charge/discharge cycle. As shown in FIG. 1, during a charge/discharge cycle, the electrolyte in each separate storage tank can be transported through the corresponding chamber. In the charging cycle, by applying electric power to the cell, the active material contained in the second electrolytic solution undergoes one or more electron oxidation, and the active material in the first electrolytic solution undergoes one or more electron reduction. Can receive. Similarly, in the discharge cycle, the second active material is reduced and the first active material is oxidized to generate electric power.

The separator can be a porous membrane in some embodiments, and/or an ionomer membrane in various other embodiments. In some embodiments, the separator can be formed of an ion conducting polymer. The separator or membrane, regardless of its type, can be conductive to various ions.

The polymer membrane can be an anion conducting or cation conducting electrolyte. When referred to as an "ionomer," the term refers to a polymeric membrane that contains both electrically neutral and ionized repeating units, where the ionized repeating units are pendant groups. backbone). Generally, the proportion of ionized units can range from about 1 mol% to about 90 mol%. For example, in some embodiments, the content of ionized units is less than about 15 mol%, and in other embodiments, the ionic content is higher, eg, greater than about 80 mol%. In yet another embodiment, the ionic content is defined by an intermediate range, such as a range of about 15 to about 80 mol %. Examples of the ionized repeating unit in the ionomer include anionic functional groups such as sulfonic acid groups and carboxylic acid groups. These functional groups can be balanced in charge by monovalent or divalent or higher cations such as alkali or alkaline earth metals. Ionomers also include polymer compositions to which quaternary ammonium, sulfonium, phosphazenium, and guanidinium residues or salts have been added or incorporated. Suitable examples will be familiar to those skilled in the art.

In some embodiments, the polymer that can be utilized as a separator can include a highly fluorinated polymer backbone or a perfluorinated polymer backbone. Specific polymers that can be utilized in this disclosure include copolymers of tetrafluoroethylene and one or more fluorinated acid functional comonomers. This copolymer is commercially available from DuPont as NAFION® perfluorinated polymer electrolyte. Other available perfluorinated polymer, tetrafluoroethylene and _{FSO 2 -CF 2 CF 2 CF 2} CF 2 copolymers -O-CF = CF _2, Flemion (FLEMION) (R) and Selemion ( SELEMION) (registered trademark).

Further, a substantially non-fluorinated membrane modified with a sulfonic acid group (or a cation exchange sulfonic acid group) can be used. Examples of such a membrane include those having a substantially aromatic skeleton, and may include, for example, polystyrene, polyphenylene, biphenyl sulfone (BPSH), or a thermoplastic material such as polyether ketone and polyether sulfone. it can.

A porous membrane for a battery separator can also be used as the present separator. Since such membranes do not wait for ionic conductivity by themselves, they are usually impregnated with additives to function as separators. Generally, these membranes contain a mixture of polymer and inorganic filler and have many open pores. Suitable polymers include, for example, high density polyethylene, polypropylene, polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE). Suitable inorganic fillers include silicon carbide matrix materials, titanium dioxide, silicon dioxide, zinc phosphide and ceria.

The separator can also be formed of polyester, polyetherketone, poly(vinyl chloride), vinyl polymers and substituted vinyl polymers. These can be used alone or in combination with any of the aforementioned polymers.

The porous separator is a non-conductive film that enables charge transfer between both electrodes via an open channel filled with an electrolytic solution. However, this permeability increases the probability that the active material will pass through the separator from one electrode to the other, causing cross-contamination and/or reduced cell energy efficiency. The degree of this cross-contamination, among other features, is pore size (effective diameter and channel length), pore characteristics (hydrophobic/hydrophilic), electrolyte properties, and pore wetness with electrolyte. It can be determined by sex.

The pore size distribution of the porous separator is generally sufficient as long as it substantially prevents active material crossover between the two electrolytic solutions. The average pore size distribution of suitable porous membranes can be about 0.001 nm to 20 μm, more typically about 0.001 nm to 100 nm. The pore size distribution of the porous membrane can be fairly wide. In other words, the porous membrane can include a first plurality of pores having a very small diameter (less than approximately 1 nm) and a second plurality of pores having a very large diameter (greater than approximately 10 μm). If the size of the pores increases, the amount of crossover of the active material may increase. The substantial preventive power of the active material from crossover of the porous membrane can be determined by the relative difference between the average pore size and the active material size. For example, if the active material is a metal-based coordination complex, the average diameter of the coordination complex can be about 50% larger than the average pore size of the porous membrane. On the other hand, if the porous membrane had a substantially uniform pore size, then the average diameter of the coordination complex could be about 20% larger than the average pore size of the porous membrane. If the coordination complex is further coordinated with at least one water molecule, the average diameter of the coordination complex will be even larger. The diameter of the coordination complex with at least one water molecule is what is generally considered to be the hydrodynamic diameter. In this embodiment, this hydrodynamic diameter is approximately at least about 35% larger than the average pore size. On the other hand, if the average pore size is substantially uniform, then the hydrodynamic diameter can be about 10% larger than the average pore size.

In some embodiments, the separator can also include a reinforcing material to enhance stability. Suitable reinforcing materials include nylon, cotton, polyester, crystalline silica, crystalline titania, amorphous silica, amorphous titania, rubber, asbestos, wood, or any combination thereof.

The separator in a flow battery of the present disclosure is less than about 500 μm, less than about 300 μm, less than about 250 μm, less than about 200 μm, less than about 100 μm, less than about 75 μm, less than about 50 μm, less than about 30 μm, less than about 25 μm, less than about 20 μm, It can have a film thickness of less than about 15 μm, or less than about 10 μm. Suitable separators include those that allow the flow cell to operate at current efficiencies of greater than about 85% and current densities of 100 mA/cm ² when the separator has a thickness of 100 μm. In a further embodiment, the flow battery has a current efficiency of greater than 99.5% when the separator has a thickness of less than about 50 μm and a current efficiency of greater than 99% when the separator has a thickness of less than about 25 μm. And can operate with a current efficiency greater than 98% when the separator has a thickness less than about 10 μm. Thus, suitable separators include those that allow flow cells to operate at voltage efficiencies above 60% and current densities of 100 mA/cm ² . In further embodiments, suitable separators include those that allow the flow battery to operate with a voltage efficiency of greater than 70%, greater than 80%, or greater than 90%.

The diffusivity of the first active material and the second active material through the separator is less than about 1×10 ⁻⁵ mol/cm ² /day, less than about 1×10 ⁻⁶ mol/cm ² /day, less than about 1 Less than ×10 ^-7 mol/cm ² /day, less than about 1×10 ^-9 mol/cm ² /day, less than about 1×10 ^-11 mol/cm ² /day, less than about 1×10 ^-13 mol/cm ² Per day, or less than about 1×10 ⁻¹⁵ mol/cm ² /day.

The flow battery can also include an external electrical circuit electrically connected to the first electrode and the second electrode. This circuit can charge and discharge the flow battery during operation. References to the sign of the net ionic charges of the first active material, the second active material, or both active materials refer to both the oxidized and reduced forms of the redox active material under conditions where the flow battery is operating. It relates to the sign of the net ionic charge. A further exemplary embodiment of the flow battery provides: That is, (a) the first active material carries a net positive or negative charge and can be in an oxidized or reduced form for potentials within the negative operating potential of the system, whereby The oxidized or reduced form of the obtained first active material has the same charge sign (positive or negative) as the first active material, and the ionomer film also has a net ionic charge of the same sign, (b) The second active material carries a net positive or negative charge and may be in an oxidized or reduced form for potentials within the positive operating potential of the system, which results in a second resulting The oxidized or reduced form of the active material has the same charge sign (positive or negative sign) as the second active material and the ionomer film also has a net ionic charge of the same sign, or (a) and Both of (b). By making the charges of the first active material and/or the second active material and the ionomer film coincide with each other, high selectivity can be obtained. More specifically, by matching the charges in this manner, the molar flux of the ions derived from the first active material or the second active material passing through the ionomer film is less than about 3%. , Less than about 2%, less than about 1%, less than about 0.5%, less than about 0.2%, or less than about 0.1%. The term "molar flux of ions" refers to the amount of ions that pass through the ionomer membrane and balance the charge carried by the external electric/electron stream. That is, the flow battery is operable or operates while substantially blocking the active material by the ionomer membrane. Such blocking can be facilitated by the matching of charges.

A flow battery in which the present disclosure is incorporated can have one or more of the following operating characteristics. That is, (a) during operation of the flow battery, the first active material or the second active material contains less than about 3% of the molar flux of ions passing through the ionomer membrane, and (b) the round-trip current efficiency is Greater than about 70%, greater than about 80%, or greater than about 90%, (c) having a reciprocating current efficiency of greater than about 90%, (d) either a first active material or a second active material. The sign of the net ionic charge of either or both does not differ between its oxidized and reduced forms and matches the sign of the ionomer film, (e) the ionomer film thickness is less than about 100 μm, less than about 75 μm. Less than about 50 μm or less than about 250 μm, (f) the flow battery is capable of operating with a round trip voltage efficiency of greater than about 60% at a current density of greater than about 100 mA/cm ² , and (g) The energy density of the electrolyte is greater than about 10 Wh/L, greater than about 20 Wh/L, or greater than about 30 Wh/L.

In some cases, the user may want to obtain a higher charge/discharge voltage than that obtained from a single electrochemical cell. In such a case, some battery cells may be connected in series so that the voltage of each cell may be added. This forms a bipolar stack. Bipolar stacks are also called electrochemical stacks. As described herein, the use of bipolar plates to connect adjacent electrochemical cells into a bipolar stack allows for the transfer of electrons between adjacent cells while suppressing the transfer of fluids or gases. be able to. The positive and negative compartments of individual cells can be fluidly connected in a bipolar stack via a common positive and negative fluid manifold. In this way, by stacking a plurality of cells in series, it is possible to obtain a voltage suitable for conversion to DC application or AC application.

In additional embodiments, cells, bipolar stacks or batteries can be incorporated into larger energy storage systems. The large system optionally includes plumbing and control equipment useful in the operation of the large unit. Suitable pipes, controls and other equipment for such systems are known in the art, for example, pipes and pumps in fluid communication with the chambers to move the electrolyte in and out of each chamber, charged and discharged. A storage tank for holding the electrolyte solution. The cells, cell stacks and batteries of the present disclosure can also have an operation management system. The motion management system may be any suitable controller device, such as a computer or microprocessor, and may have logic circuits that set the operation of any of the various valves, pumps, circulation circuits, etc.

In a more specific embodiment, a flow battery system includes a flow battery (having cells or cell stacks), storage tanks and piping for containing and transporting electrolytes, control hardware and software (having a safety system). May be included) and a power conditioning unit. The flow battery cell stack realizes the switching between the charge cycle and the discharge cycle, which determines the peak power. The storage tank contains positive and negative active materials, such as the coordination complexes disclosed herein, and the capacity of the tank determines the amount of energy stored in the system. Control software, hardware and optional safety systems, including sensors, mitigation devices and other electronic/hardware control devices, as well as safeguarding devices as appropriate, for safe, autonomous and efficient operation of flow battery systems. Is guaranteed. The power regulation unit is used in the front end of the energy storage system to convert the input power voltage and current into optimum values for the energy storage system and the output power voltage and current into optimum values for the intended use. be able to. In the case of an example of an energy storage system connected to a power grid, during the charging cycle, the power conditioning unit can convert the input AC power into DC power of voltage and current suitable for the cell stack. On the other hand, in the discharge cycle, the stack produces DC power, and the power conditioning unit converts this DC power into AC power of suitable voltage and frequency for sending to the grid.

Unless defined otherwise above or otherwise understood by one of ordinary skill in the art, the definitions in the following paragraphs can be applied to the present disclosure.

As used herein, the term "energy density" refers to the amount of energy that can be stored in the active material per unit volume. Energy density refers to the theoretical energy density of energy storage and can be calculated by the following equation 1.
Energy Density = (26.8A-h / mol) × OCV × [e -] (1)
In the formula, OCV is an open circuit potential in a charged state of 50%, (26.8 A-h/mol) is a Faraday constant, and [e ⁻ ] is an active material in a charged state of 99%. Is the concentration of electrons stored in. When both the positive electrolyte solution and the negative electrolyte solution active materials mainly contain atomic species or molecular species, [e ⁻ ] can be calculated by the following equation 2.
[E ⁻ ]=[active material]×N/2 (2)
In the formula, [active material] is the lower of the molar concentration of the active material in the negative electrolyte solution or positive electrolyte solution, and N is the number of electrons transferred per molecule of the active material. Is. The related term "charge density" refers to the total amount of charge contained in each electrolyte. For a given electrolyte, the charge density can be calculated by Equation 3 below.
Charge density=(26.8 A-h/mol)×[active material]×N (3)
In the formula, [active material] and N are as defined above.

As used herein, the term "current density" refers to the total current flowing through an electrochemical cell divided by the geometric area of the electrodes of the cell, generally expressed in units of mA/cm ^2. It

As used herein, the term "current efficiency" (I _eff ) can be described as the ratio of the total charge transferred during charge to the total charge generated during discharge of the cell. The current efficiency can be a function of the state of charge of the flow battery. In some non-limiting embodiments, current efficiency can be determined when the state of charge is in the range of about 35% to about 60%.

As used herein, the term "voltage efficiency" can be described as the ratio of the electrode potential observed at a given current density to the half-cell potential of that electrode (x100%). .. The voltage efficiency may include voltage efficiency during the charging process of the battery, voltage efficiency during the discharging process, or "round trip voltage efficiency". The round-trip voltage efficiency (V _eff,RT ) at a given current density can be calculated from the cell voltage during _discharge (V _discharge ) and the voltage during _charge (V _charge ) using Equation 4 below.
V _eff,RT =V _discharge /V _charge ×100% (4)

As used herein, the terms "negative electrode" and "positive electrode" refer to electrodes that are relatively defined and in practice they operate during both charge and discharge cycles. Regardless of the potential of the negative electrode, the negative electrode operates at a more negative potential than the positive electrode, and vice versa, or is designed or intended to operate. The negative electrode may, or may not, actually operate or be designed or intended to operate at a more negative potential than the reversible hydrogen electrode. The negative electrode is associated with the first electrolyte and the positive electrode is associated with the second electrolyte, as described herein. The electrolytic solution associated with the negative electrode may be referred to as negolyte (negative electrode electrolytic solution), and the electrolytic solution associated with the positive electrode may be referred to as posolyte (positive electrode electrolytic solution).

Thus, in some embodiments of the present disclosure, a first half-cell including a first electrode, a second half-cell including a second electrode, the first half-cell and the second half-cell. A separator disposed between the battery and a first bipolar plate covering and in contact with the first electrode; and a second bipolar plate covering and in contact with the second electrode. A flow battery having a plate is provided. Here, the first electrode and the second electrode respectively cover and contact both surfaces of the separator. Further, while the first electrode or a part of the first bipolar plate contains a dielectric material, the first electrode and the first bipolar plate are continuous in the first half cell. Jointly regulates various conductive paths. As mentioned above, the contact between the first electrode and the first bipolar plate may be direct or indirect.

In various embodiments, the first electrode has an effective area such that the ratio of productive reactions to parasitic reactions during operation of the flow battery is greater than about 5. In various other embodiments, the first electrode has an effective area sized such that the ratio of productive reactions to parasitic reactions during operation of the flow battery is greater than about 10. In more specific embodiments, the ratio of productive reaction to parasitic reaction is about 15 or more, about 20 or more, about 30 or more, about 40 or more, about 50 or more, about 100 or more, about 200 or more, about 500 or more. , Or about 1000 or more.

In some embodiments, the dielectric material can reduce the amount of available area on the first electrode that can be utilized to promote parasitic reactions. In an alternative embodiment, a first electrode having a thickness of about 100 microns or less is used to bring the entire first electrode closer to the separator, which reduces the incidence of parasitic reactions and is productive. The reaction can be accelerated.

Accordingly, in some embodiments, a flow battery of the present disclosure includes a first half-cell including a first electrode, a second half-cell including a second electrode, the first half-cell and the A second half-cell and a separator disposed between the second half-cell and the second half-cell. Here, the first electrode and the second electrode respectively cover and contact both surfaces of the separator. Also, at least the first electrode has a thickness of about 100 microns or less. In some embodiments, the first electrode has an effective area sized such that the ratio of productive reactions to parasitic reactions during operation of the flow battery is greater than about 10. In a further embodiment, a flow battery comprises a first bipolar plate covering and in contact with the first electrode and a second bipolar plate covering and in contact with the second electrode. Can have Again, the contact may be direct or indirect.

In some embodiments, the dielectric material is implanted within the first electrode or within the first bipolar plate. When the dielectric material is injected inside the first electrode, the dielectric material is not in contact with the separator or the first bipolar plate. When the dielectric material is injected inside the first bipolar plate, the dielectric material is not in contact with the first electrode. In a more specific embodiment, the first bipolar plate may include a plurality of channels that are at least partially covered by the dielectric material. In some embodiments, the channels can also be completely filled (occluded) with a dielectric material.

In an alternative embodiment, the first bipolar plate may be formed of a dielectric material and a plurality of conductor posts extend through the dielectric material and contact the first electrode. it can.

In some embodiments, the first electrode is a conductive mesh including a conductive medium and the dielectric material, the conductive medium disposed on a first side of the conductive mesh. And the dielectric material is disposed on the second side of the conductive mesh. Here, the conductive medium is in contact with the separator, and the dielectric material is in contact with the first bipolar plate. A plurality of conductor posts extend through the dielectric material from the conductive mesh to the first bipolar plate.

In some embodiments, the first electrode can be the negative electrode of an electrochemical cell. In another embodiment, the first electrode can be the positive electrode of an electrochemical cell. However, the various cell configurations disclosed herein may be particularly advantageous in reducing the incidence of parasitic reactions on the negative electrode and its associated bipolar plates.

In some embodiments, the first electrode can be a catalyst layer that covers the separator. In a more specific embodiment, the catalyst layer may be discontinuous or have a predetermined porosity so as not to impair the permeability of the separator. In some embodiments, the catalyst layer can include a plurality of carbon nanotubes. In a further embodiment, the metal catalyst can be dispersed among multiple carbon nanotubes.

In the present disclosure, a related method, a method of suppressing the incidence of parasitic reaction is also implied. The method is disposed between a first half-cell including a first electrode, a second half-cell including a second electrode, and the first half-cell and the second half-cell. Forming a flow battery having a separator, a first bipolar plate covering and in contact with the first electrode, and a second bipolar plate covering and in contact with the second electrode And introducing a dielectric material into the first electrode or a part of the first bipolar plate, the first electrode and the first bipolar plate being introduced. Includes introducing a dielectric material into the first electrode or a portion of the first bipolar plate so as to jointly define a continuous conductive path within the first half-cell. Here, the first electrode and the second electrode respectively cover and contact both surfaces of the separator. In some embodiments, the dielectric material is introduced into the first electrode or the first bipolar plate by spraying a solution of the dielectric material onto the first electrode or the first bipolar plate. To be done.

Other related methods of reducing the incidence of parasitic reactions include providing a separator, depositing a catalyst layer on at least a first face of the separator, and a flow battery having the catalyst layer. Forming, comprising forming the flow cell, wherein the catalyst layer is in contact with a bipolar plate in at least a first half cell of the flow cell.

Yet another related method of suppressing the incidence of parasitic reactions may include forming a flow battery having a first electrode in contact with the separator and having a thickness of about 100 microns or less.

Although the present disclosure has been described with reference to the above disclosed embodiments, those skilled in the art will readily recognize that these embodiments are merely illustrative of the present disclosure. It should be understood that various modifications can be made without departing from the spirit of the present disclosure. This disclosure may be modified by incorporating any number of variations, modifications, substitutions, or equivalent arrangements, which are not included in the above description but are appropriate for the spirit and scope of the disclosure. Furthermore, although various embodiments of the present disclosure have been described, it should be understood that aspects of the disclosure may include only some of the described embodiments. Therefore, the present disclosure should not be considered limited by the above description.

Claims (15)

A first half-cell comprising a first electrolyte and a porous first electrode;
A second half-cell including a second electrolyte and a second electrode;
A separator arranged between the first half-cell and the second half-cell, wherein each of the first electrode and the second electrode covers and covers both sides of the separator. In contact with the separator,
A first bipolar plate covering and in contact with the first electrode, and a second bipolar plate covering and in contact with the second electrode,
By covering a part of the inner surface of the pores of the first electrode with a dielectric material , a part of the inner surface of the pores covered with the dielectric material by the dielectric material is formed. Contact is hindered but the flow of the first electrolyte solution through the first electrode is not hindered , and the first electrode and the first bipolar plate are continuous in the first half cell. Flow battery that jointly defines a specific conductive path. Wherein the dielectric material, wherein are injected into the portion of the first electrode, the flow cell according to claim 1. The dielectric material is injected inside the first electrode,
The flow battery of claim 2, wherein the dielectric material is not in contact with the separator or the first bipolar plate. Dielectric material is also injected inside the first bipolar plate,
The flow battery according to claim 2, wherein the dielectric material injected into the inside of the first bipolar plate is not in contact with the first electrode. The flow battery of claim 4, wherein the first bipolar plate includes a plurality of flow channels that are at least partially coated with a dielectric material injected into the first bipolar plate . The flow battery of claim 1, wherein the first bipolar plate includes a plurality of conductor posts that extend through the dielectric material and contact the first electrode. The first electrode includes a conductive mesh including a conductive medium and the dielectric material,
The conductive medium is disposed on a first side of the conductive mesh and is in contact with the separator,
The dielectric material is disposed on the second side of the conductive mesh and is in contact with the first bipolar plate,
The flow battery of claim 1, wherein a plurality of conductor posts extend through the dielectric material from the conductive mesh to the first bipolar plate. The flow battery according to claim 1, wherein the first electrode is a negative electrode. A first half-cell comprising a first electrolyte and a porous first electrode;
A second half-cell including a second electrolyte and a second electrode;
A separator arranged between the first half-cell and the second half-cell, wherein each of the first electrode and the second electrode covers and covers both sides of the separator. In contact with the separator,
A first bipolar plate covering and in contact with the first electrode, and a second bipolar plate covering and in contact with the second electrode;
Forming a flow battery having:
The part of the inner surface of the pores of the first electrode was to be coated with a dielectric material, said coating by, coated with the dielectric material of the inner surface of the pores with the first electrolyte by said dielectric material The contact between the first electrode and the first bipolar plate is prevented, but the flow of the first electrolytic solution passing through the first electrode is not hindered. A method comprising coating a portion of the inner surface of the pores of the first electrode with a dielectric material so as to jointly define a continuous conductive path within the cell. A portion of the first electrode contains the dielectric material,
Coating with the dielectric material includes injecting the dielectric material into the first electrode,
10. The method of claim 9 , wherein the dielectric material is not in contact with the separator or the first bipolar plate. A portion of the first bipolar plate also contains a dielectric material,
The be coated with a dielectric material comprises injecting induced material charge inside the first bipolar plate,
The method of claim 9 , wherein the dielectric material is not in contact with the first electrode. The dielectric material contained in a portion of the first bipolar plate is injected into the plurality of channels in said first bipolar plate, the flow path is coated with induced material cost, to claim 11 The described method. The dielectric solution portion of the inner surface of the pores by spraying on the first electrodes a material is coated with the dielectric material, The method of claim 9. 10. The method of claim 9 , wherein the first bipolar plate includes a plurality of conductor posts extending through the dielectric material, the plurality of conductor posts contacting the first electrode. The first electrode includes a conductive mesh including a conductive medium and the dielectric material,
The conductive medium is disposed on the first surface of the conductive mesh and is in contact with the separator,
The dielectric material is disposed on the second side of the conductive mesh and is in contact with the first bipolar plate,
The method of claim 9 , wherein a plurality of conductor posts extend through the dielectric material from the conductive mesh to the first bipolar plate.